Smectites are poorly crystalline minerals which cannot be easily characterized by traditional methods, despite more than 100 years of effort. Accurate characterization requires multiple spectroscopic and physical techniques. The result is an average crystal chemical picture.

Figure at right is one such estimation of the array of octahedral cations in the Nibost smectite as deduced from analysis of the infrared spectra. The tetrahedral sheets have not been included in this representation.

See Gates 2008 Clays and Clay Minerals, 56:11-23 for further details.

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Pore-filling reactions in bentonites, due to alkaline-induced dissolution/precipitation reactions, can enhance the barrier performance of geosynthetic clay liners.

The strong water absorption capability of smectites underpins the fact that bentonites are one of the most useful industrial minerals. Water is held in many different energy states, so that some is released easily, but some is retained strongly.

Bentonites are widely used as components of environmental barriers in landfills, tailings dams and impoundments. Not all bentonites behave the same when reacting with typical leachates in the environment, which means that each bentonite should be ‘compatibility’ tested and assessed for specific applications.

The above graph depicts the ratio of Fluid Loss at each concentration of NaCl to its value in deionised water. The fluid loss of even high performance bentonites can increase by 10—20 times in 5 M NaCl (about 10x the salinity of seawater). Such behavior must be accounted for in designs by environmental engineers.